A photoresist dispensing system used in a photoresist coating machine includes a pump, a sucking-back valve, a solenoid valve, a first pump speed controller, a second pump speed controller and a sucking-back speed controller. The pump is used to transport photoresist and spray a substrate. The sucking-back valve is used to suck back liquid photoresist from a transporting duct end. The solenoid is used to activate or inactivate the pump and the sucking-back valve. The first and the second pump speed controllers are separately coupled between the pump and the solenoid valve, and the sucking-back speed controller is coupled between the sucking-back valve and the sucking-back speed controller is coupled between the sucking-back valve and the route, where is between the pump and the second pump speed controller. Hence, the sucking-back valve produces a sucking force after the pump is inactivated and releases a sucking force after pump is activated.